June 22, 2010

Life and art, sand and glass: the wonders of Difflugia

Inspiration has no respect for scale: the images from the Hubble telescope
are no more or less wondrous than those from the nano-world. An exhibition at
London's Natural History Museum, titled "The Deep," explores the wonders of life
in the oceans on all scales, macro, meso, and micro, and included are some
exhibits that have been gathering dust in the museum's cavernous store rooms for
decades. The creatures in the illustration above are Difflugia
pyriformis, a common, but as is so often the case, rather extraordinary,
microbe. Difflugia are members of a genus of amoeba or protozoa,
single-celled organisms; pyriformis means pear-shaped (as in "things
have gone pyriform"), and all Difflugia share an amazing and mysterious
common skill that we shall come to shortly.

The central image above is a real Difflugia pyriformis - the ones on
either side are glass sculptures of it. These exquisite examples of hand-blown
glass biological sculptures are amongst those treasures that have been hidden
away at the museum since the Victorian enthusiasm for such things was no longer
in vogue. This meticulous art was the work of father and son craftsmen, Leopold
and Rudolf Blaschka, whose studio in Dresden was a prolific source of fine glass
work during the second half of the nineteenth century. The family had a long
tradition of glass-making, originally in Venice, home of the famous Murano glass
wrought from the quartz sands and pebbles that cascaded out of the eroding Alps.
They moved to Northern Bohemia, now in the Czech Republic, then the centre of
craftsmanship in glass and gemstones - making glass eyes for taxidermists was
amongst their specialities. Leopold's interest in natural history led to him
beginning to make models of flowers in glass and this work became a commercial
mainstay of the business when the Dresden Natural History Museum ordered a
series of glass sea anemones for their exhibits, and further commissions began
to come in from museums around the world. The young Rudolf joined his father in
the workshop, and by 1888 the two of them , working alone, had produced a
catalogue of more than 400 models, including not only anemones but also squids,
sea octopi, cuttlefish, sea squirts and jellyfish; the demand for these lifelike
representations reflected the poor preservation methods for real specimens. The
Blaschkas' methods were unique and creative, using paint and powdered glass to
add further texture and colour to the meticulous sculptures. Examples in the
Boston Museum of Natural History were spotted by George Lincoln Goodale who was
preparing to set up the Harvard Botanical Museum; Goodale travelled to Dresden
and persuaded the Blaschkas to return to their early plant and flower
sculptures, the results eventually being the 4000 or so exhibits for the now famous
collection. Rudolf continued to make glass sculptures until a couple of
years before his death in 1929; the family secrets went to the grave with
him.

In making their Difflugia pyriformis sculptures, the Blaschkas may
well have used as a reference illustrations from Joseph Leidy's monograph,
"Fresh-Water Rhizopods of North America," published in 1879. A plate
illustrating nothing but examples of this species is below, together with a live
example:

But why should an amoeba like Difflugia pyriformis have such a
strange appearance in Leidy's plates, the Blaschkas' work, and in real life?
Simply because, like all Difflugia, it builds its shell out of sand.
There is thus a delicious self-reference in the sculptures: to replicate the
appearance of the amoeba's sandy shell, the Blaschkas used shards of glass, much
of which they made themselves, from, of course, sand.

Now, to describe the shell of Difflugia pyriformis as being
constructed from grains of sand is not quite accurate - the creature itself is
only as large as a single grain of fine sand, and so its construction materials
are finer, strictly, than sand. But there are countless species of
Difflugia, all tiny but some larger than others. Take, for example,
Difflugia coronata:

...I give you this structure: It is a sphere composed of a few hundred stones
cemented together, on top of which there are seven or eight sturdy spikes, each
a cairn of stones, larger ones at the base, smallest at the tip creating a sharp
point. At the bottom of the sphere there is a large circular hole ornamented
with a pleated collar of particles too small to be distinguishable from the
cement that binds them. The diameter of the whole dwelling, for that is what it
is, is about 150 thousandths of a millimetre. Smaller than the punctuation mark
at the end of this sentence. It is the portable home of Difflugia
coronata, a species of amoeba.

An amoeba, as you very likely know, is a single celled organism. The one cell
does everything. It feeds, excretes, moves and reproduces and, in this species,
it also builds a home. The cell has no nervous system at all, let alone a brain.
Can its extraordinary achievement really be said to be building? Well, as the
organism's amorphous bulk glides gently round the bottom of some pond, engulfing
food particles and growing, it also picks up tiny sand grains that accumulate as
a mass inside it. When it grows to a certain size, the cell then reproduces by
dividing its body equally into two. One of these inherits the ancestral home;
the other is left the bundle of building material. These stones, we know not
how, are then moved to the body surface and arranged to create the distinctive
architecture of this species. Just enough particles of the right sizes, big and
small, have been picked up to accomplish this.

So, here is a single-celled wonder that ingests sand grains and then divides,
one half to all intents and purposes turning itself inside-out to
create its shell. And we really don't understand how it does it.
Inspiration for the art of the Baschkas - and for us? In the same vein of what
we might learn from nature's construction methods, reviewed in Hansell's book,
the "Ask Nature" project on biomimetic
application ideas asks: what are the possibilities of building from the
inside out, perhaps for self-healing materials? And what is the glue
that Difflugia uses? These are echoes of a couple of nature's wonders
that I've written about before, Bacillus pasteuriimending
concrete, and sandcastle
worms using natural superglue. Inspiration comes on every scale.

Comments

Difflugia is one of several genera of amoebozoa that produce shells or tests from granules of sand. These are swallowed by the cell and during the process of budding or fission they pass into the daughter, where they are joined by organic cement.